A research program is proposed on the induction and consequences of protein synthesis errors in eukaryotic cells. This program is based on findings made in our laboratory, concerning the stimulation of misreading by paromomycin, and certain other structurally related members of the aminoglycoside antibiotics. We propose to define the chemical structure necessary for misreading and to show that these molecules act at the level of the ribosome. These studies will be complemented by measurements of the binding of paromomycin to eukaryotic ribosomes. Studies on misreading will be extended to other classes of antibiotics, distinct from the aminoglycosides. Our work has shown that paromomycin can produce phenotypic suppression of nonsense mutations in yeast. Thus, this drug may be useful for the identification of nonsense mutants, generally, in eukaryotic cells. We have isolated paromomycin-resistant mutants of the ciliated protozoan, Tetrahymena. These could be useful in a long-term strategy to develop a system of nonsense mutations and nonsense suppressors in this organism, and to study the genetics of ribosome biogenesis. Finally, Tetrahymena responds to paromomycin by induction of several polypeptides. We are testing the hypothesis that one of these is a protease, capable of degrading abnormal protein.